Electrical Measurements and Instrumentation Full course on slide share

1. Wattmeter and Energy
Meter
Electrical Measurements and Instrumentation (EE-336)

2. Contents
• Electrical Power
• Power Measurement
• Wattmeter in General and DC Measurement
• Power in AC Circuits
• Electron-dynamometer type wattmeter
• Construction of ED wattmeter
• Operation of ED wattmeter
• Phenomena of Induction
• Induction Type instrument
• Single Phase Energy meter
• Construction
• Operation
• Testing of Energy Meter

3. Electrical Power
• The rate of doing electrical work or equivalent mechanical or thermal
work
• P=W/t
• Unit is Watt for real power dissipation
• It can be Var or VA depending upon the nature of energy storage or
dissipation
• KVA, KWA and KVar are larger units
• Normally when we talk about power, we mean real power or the
product or Irms and Vrms

4. Power Measurement
P=IrmsVrms
1. In DC. RMS values and Instantaneous values are equal so we can
write P=IV
2. Measure I and V individually and then multiply it
• In this method, the first connected instrument indicates the amount of power
delivered to the device as well as the power spared for the next instrument
connected.
3. Measure the effect of I and V on a single entity

5. Wattmeter in General
The equivalent resistance changes for each path while connecting Type a or Type b

6. Example
Solve from Book and use your knowledge to understand the connections

7. Power in AC
• P=IrmsVrms
• P=ImaxVmaxCosΦ
• S=i(t)v(t)

8. Construction of Electro-dynamometer type
wattmeter

9. Construction of Electro-dynamometer type
wattmeter
• Fixed coils system
• Moving Coil system
• Moving and restoring system
• Damping system
• Shielding system

10. Operation of Wattmeter in AC
Rv is connected because usually resistance of PC is very low and it may short circuit the path of current that is leading to the LOAD

11. Phenomena of Induction
• Induction Principle
• The live wire induces some magnetic field in a metal surface or another wire
or core – then pushes the same magnetized region with its magnetic field
because the already induced magnetic field is in opposite direction to the live
wires magnetic field
• Induction motor
• A motor in which the excitation is supplied to its one side and the rotation is
observed on its electrically separated but magnetically connected side
• Rotating/Moving Transformer
• An induction motor and such instruments are also termed as rotating
transformers because its secondary coil is short circuited and it moves/rotates
to compensate its short circuit current

12. Induction type instruments
• The operations of induction-type instruments depend on the
production of torque due to the interaction between a flux Φ1
(whose magnitude depends on the current or voltage to be
measured) and eddy current induced in a metal disc or drum by
another flux Φ2 (whose magnitude also depends on the current or
voltage to be measured).
• Since the magnitude of eddy current also depends on the flux
producing them, the instantaneous value of the torque is
proportional to the square of current or voltage under
measurement and the value of mean torque is proportional to the
mean square value of this current or voltage.

13. Single Phase Energy Meter

14. Construction
1. Voltage coil
2. Current Coil
3. Stator
4. Aluminum
Desk
5. Rotor Brake
magnet
6. Spindle with
worm gear
7. Display Dial

15. Sections of Energy Meter
• Operating
• Current (series) coil
• Voltage (shunt) coil
• Moving
• Aluminum Desk
• Breaking
• Desk
• Brake (magnetic)
• Registering
• Revolving gears

16. Operating an Energy meter

17. Testing of Energy Meter

18. Thanks